This invention relates generally to heat exchanger apparatus and more particularly to gas turbine heat exchanger apparatus.
Gas turbine engines generally use heat exchangers to recover some of the heat of the turbine exhaust gases for transfer to the compressor discharge air before it enters the turbine combustion chamber, which provides for greater fuel economy. However, during turbine start-up conditions, for example, the turbine exhaust gases can reach very high temperatures which can cause very high thermal gradients between the exhaust gas inlet surface and the outlet surface of the heat exchanger core, producing thermal stresses resulting in splitting and cracking of the core. In order to eliminate such a disadvantage some prior heat exchanger apparatus included a heat sink positioned ahead of the heat exchanger core gas inlet surface in the path of flow of the turbine exhaust gases which temporarily reduced the gas temperature, preventing thermal gradients during engine start-up. However, use of such a heat sink, though reducing the gas inlet surface temperature of the heat exchanger core, also undesirably reduced the temperature of gas impinging on air outlet manifolds conveying the compressor discharge air, thus lowering fuel economy.
Examples of prior art heat exchange devices are disclosed in the following U.S. Pat. Nos. 2,492,788 to Dennis; U.S. Pat. No. 2,891,774 to Theoclitres; U.S. Pat. No. 3,263,744 to MacKeown; U.S. Pat. No. 3,289,743 to Biro; U.S. Pat. No. 3,322,189 to Topouzian; U.S. Pat. No. 3,326,214 to McCoy; U.S. Pat. No. 3,507,115 to Wosika; and U.S. Pat. No. 3,528,783 to Haseldon.